This invention is primarily directed to reconstituted articular cartilage, which is a specialized tissue found at the end of articulating bones. Cartilage, unlike other connective tissues, lacks blood vessels, nerves lymphatics and basement membrane. It is responsible for the distribution of load resistance to compressive forces, and the smooth gliding that is part of joint function.
Cartilage is composed of chondrocytes which synthesize an abundant extracellular matrix, which is composed of water, collagens, proteoglycans and noncollagenous proteins and lipids. Collagen serves to trap proteoglycans and to provide tensile strength to the tissue.
Damage of cartilage produced by disease, such as arthritis, or trauma is a major cause of physical deformity and debilitation. In medicine today, the primary therapy for loss of cartilage is replacement with a prosthetic material, such as silicone for cosmetic repairs, or metal alloys for joint relinement. Placement of prostheses is commonly associated with significant loss of underlying tissue and bone without recovery of the full function allowed by the original cartilage, as well as the irritating presence of a foreign body. Other long term problems associated with a permanent foreign body can include infection, erosion and instability
Very little has ever been actually used to replace the cartilage overlaying bone surfaces. To date, the growth of new cartilage from either transplantation of autologous or allogeneic cartilage has been largely unsuccessful. Microscopic islands of cartilage formation have recently been demonstrated histologically in vivo by implanting recombinant bone morphogenic protein, as reported by J. M. Wozney, et al., Science, 242, 1528-1534, (Dec. 16, 1988). Limited success has been achieved in making neocartilage using free autogenous grafts of perichondrial flaps, as described by J. Upton, Plastic and Reconstructive Surgery, 68(2), 166-174; (August 1981).
It is also known in the art to use cells harvested from an organism for implantation into the same or a different organism. Such techniques are shown is U.S. Pat. Nos. 4,299,819, 4,418,691, 4,458,678, 4,505,266, 4,553,272, 4,804,382, 4,883,487, 4,904,259, 4,960,423, 5,015,584, 5,035,708, and 5,041,138 the disclosures of which are expressly incorporated herein by reference. In these references, the cells are seeded on a biocompatible support material and implanted into a desired site for tissue repair, with or without a step of cell cultivation in vitro, depending upon the type of tissue being replaced and the extent of tissue damage at the site needing repair. The limitations of his technique are associated with the substrate material. Typically, bioabsorbable substrates are used for cell seeding. During cell cultivation in vitro, portions of these substrate materials are absorbed, leaving a support material for implantation which does not have the strength and resiliency to function as a prosthetic device at the site of tissue damage while additional tissue ingrowth and cell division takes place.
The provision of a suitable support material is a critical part of the in vitro cell cultivation technique. This is because most types of tissue will not grow or divide in suspension; a solid support is necessary for the cells to perform their normal functions. However, because the growing cells must receive nutrients from the nutrient media and eliminate cell waste products, all without a circulatory system which normally performs this function, the support upon which the cells are placed must allow for this exchange. Additionally, many cell cultures require a support coated with materials which form a part of the extracellular matrix, a collection of polysaccharides and proteins which exist outside the cell's membrane.
Cheung (in vitro Cell. Dev. Biol. 21:353, 1985) teaches a method of culturing canine chondrocytes on porous hydroxyapatite ceramic granules. The cells reportedly proliferated and secreted metachromatic extracellular matrix for up to 13 months. An agarose gel matrix has also been described as suitable for the in vitro culture of human chondrocytes (Delbruck et al., Conn. Tiss. Res. 15:155, 1986). Watt and Dudhia (Differentiation 38:140, 1988) disclose a composite gel of collagen and agarose for the culture of porcine chondrocytes. The composite gel prevented chondrocytes spreading. However, virtually no extracellular matrix was secreted in the low density culture composite gels.
Macklis et al. (in vitro Cell. Develop. Biol. 21:180, 1985) teach a collagen surface for culturing peripheral nervous system cells, comprising collagen derivatized to polystyrene plastic culture dishes. Macklis et al. disclose that the derivatized coating process yielded enhanced collagen adhesion and increased long term survival of cultured nerve cells, compared to collagen coating produced by absorption techniques.
U.S. Pat. No. 5,376,118, relates to the use of a support material fabricated from semiabsorbable, composite yarn as a support for cell growth in vitro. The support comprises a nonabsorbable, elastic core yarn and at least one absorbable, relatively inelastic sheath yarn imparting transverse strength to the composite yarn. The cells that can be grown on the support allegedly encompass endothelial cells, epidermal cells, muscle cells, bone cells, and cartilage cells.
U.S. Pat. No. 5,326,357, relates to the use of a substrate for chondrocyte cell growth in vitro. The substrate that is employed is a synthetic substrate, Millicell.RTM.-CM, coated with attachment factors.
U.S. Pat. No. 5,041,138, relates to a method for making a cartilaginous structure by use of a biocompatible, biodegradable synthetic polymeric matrix for chondrocyte cell growth in vitro , and its use for replacing defective or missing cartilage.
To date, none of the aforementioned methods of cartilage growth and replacement have found wide acceptance. As can be seen from the descriptions, the methods that use chondrocyte cell growth in vitro, rely upon synthetic support media that are foreign to the body, resulting in problems associated with the introduction of foreign compositions into the body.
A need therefore exist for a method for growing chondrocytes ex vivo by use of a supportive substrate that will find universal acceptance upon implantation for reconstructive use, while providing the characteristics necessary for cell growth in vitro.